In order to treat cancers, there have been recently adopted chemical therapy using various anticancer agents, immunotherapy for promoting the production of antibodies against cancer cells, surgical therapy for extracting cancer cells, radiotherapy for killing cancer cells by irradiation, etc. However, as these therapies have been developed, the surgical operations or radiotherapy technically suffer their limits, and cannot effectively inhibit the metastasis of the cancers. On the other hand, although the chemical therapy directly acts upon the cancer cells with use of the anticancer agents, many of the anticancer agents then cause harmful side effects even upon normal cells of a host. Therefore, the chemical therapy is not necessarily effective for the metastasis of the cancer. Further, no excellent effects against the metastasis of the cancers have not been seen in the case of the immunotherapy which is to treat the cancer. Although the therapeutic effects against original cancers have been largely enhanced, not a few patients become dead by metastasized cancers provoked by the metastasis of cancer cells, even if the original cancers are completely cured. In order to inhibit the metastasis of the cancers, there has strongly demanded development of medicines for inhibiting the metastasis of cancer cells. It is considered that the cancer cells metastasize over a wide area through being adhered to cell membranes of tissues such as mesenteries.
Although it is recognized that a medicine for inhibiting the metastasis of cancer cells has an effect to inhibit the metastasis of the cancer cells when sizofiran is used in combination with a chemotherapy agent, a medicine has not been commercially available to inhibit the metastasis of cancer cells when used alone. Further, although JP-A 60-190,791, JP-A 61-83,125 and JP-A 62-223,124 disclose cancer metastasis-inhibiting actions with sialic acid derivatives, they fail to describe sialic acid or its derivative used as an effective ingredient in the present invention or the cancer metastasis-inhibiting action thereof.